Variable color display device and projection means therefor

ABSTRACT

A display device for presenting a visual indication of pressure, said device comprising a support capable of supporting a layer of liquid crystalline material thereon, said material having a characteristic of selective light scattering which is variable in accordance with applied deformational stress, and means for applying deformational stress to said material.

United State Sharpless 1 Oct. 30, 1973 1 VARIABLE COLOR DISPLAY DEVICEAND PROJECTION MEANS THEREFOR [75] Inventor: Edward N. Sharpless,Pitcairn, Pa.

[73] Assignee: Liquid Crystal Industries, Inc.,

Turtle Creek, Pa.

[22] Filed: May 27, 1970 [21] Appl. No.: 40,889

[52] US. Cl. 350/160 LC, 40/1062] 40/l06.22, 40/106.51, 40/l06.52,350/149 [51] Int. Cl. G021 1/28 [58] Field of Search 40/106.21, 106.23,40/106.52, 106.54; 350/160 LC, 149; 356/32 [56] References Cited UNITEDSTATES PATENTS 3,701,368 10/1972 Stern 350/160 LC 3,597,043 8/1971Dreyer 350/149 3,590,371 6/1971 Shaw, Jr. 350/160 3,620,889 11/1971Baltzer 350/160 3,511,086 5/1970 Woodmansee 350/160 3,533,399 10/1970Goldberg et a1. 350/160 3,441,513 4/1969 Woodmansee 350/160 LC 3,464,1329/1969 Matise 40/106.52

OTHER PUBLICATIONS J. L. Fergason, Liquid Crystals, Scientific AmericanVol. 211, Aug. 1964, pp. 77-82 & p. 85.

Materials Engineering, J. A. Mock, Feb. 1969, pp. 66-67.

Product Engineering, A. J. Parisi, July 1968, pp. 19-25.

Liquid Crystals," Product Engineering, Vol. 35, 12/21/64, pp. 56-57.

E. J. Klein, A. P. Margozzi, Apparatus for the Calibration of ShearSensitive Liquid Crystals" Rev. of Sci. Inst., Vol. 41, No. 2, 2/70, pp.238-239.

Porter & Johnson, .1. of Applied Physics, Vol. 34, No. 1, 1/63, pp.51-59.

Fergason et al., Liquid Crystals & Their Applications,Electro-Technology 1/70, pp. 41-50.

Primary Examiner-Ronald L. Wibert Assistant Examiner-Paul K. GodwinAttorney-Don J. Smith [57] ABSTRACT A display device for presenting avisual indication of pressure, said device comprising a support capableof supporting a layer of liquid crystalline material thereon, saidmaterial having a characteristic of selective light scattering which isvariable in accordance with applied deformational stress, and means forapplying deformational stress to said material.

12 Claims, 9 Drawing Figures Patented Oct. 30, 1973 3,768,886

Sheets-Sheet 2 y Fdwand M f/zagoess @QZGZQQ W VARIABLE COLOR DISPLAYDEVICE AND PROJECTION MEANS THEREFOR The present invention relates to anunexpected color display or aesthetic device and to projection means forprojecting and/or varying the color patterns produced by the device ofthe character described for display, advertising, aesthetic,entertainment or decorative effects or purposes.

Devices for displaying color patterns for various purposes are legion.These devices usually employ various colored materials or surfaces,color filters or simply lights of various colors. Many of these devicesare capable only of displaying colors or color patterns of anunnaturally fixed or varying nature, and their usefulness is therebylimited. Particularly in displays for decorative or aesthetic purposes,the "novelty wears off all too soon.

Color display devices in the form of various kinds of light projectingmachines are likewise available for use in advertising, entertainmentand in the purely decorative field. For the most part, these machinesrely on solid crystalline or plastic colored materials, photographicslides, systems of mirrors with color filters attached, movable arraysof color filters, or simply lights of various colors which may bemovably disposed or otherwise sequenced to illuminate the object or areawith the intended color pattern or patterns. While some of thesemachines work reasonably well in a limited range of applications, themachines usually are complex in construction owing to mechanicalrepetition of various components. The available color patterns or colorvariation is severely limited in most cases. The colors or colorpatterns are usually overly brilliant, cold, or otherwise un-natural intheir hues and intensities.

In most color display devices, particularly those adapted for theprojection of colored light, there is the frequent requirement thatseveral such devices or systems be used to approach the desiredaesthetic or decorative effects. The number of moving components ofthese systems are thereby multiplied, leading to maintenance problems.When several such light systems are utilized, a time synchronization isoften required, particularly when one attempts to associate music with achanging color display or an analogous dynamic lighting system. Thisobjective is difficult to accomplish with conventional systems owing tolarge numbers of moving parts and other practical difficulties.Moreover, the potential variation in color patterns has been severelylimited for the reasons pointed out above.

In many other fields of endeavor, it is desired to illuminate relativelylarge areas in varying color patterns. For example, in the field oftheatrical lighting, various types of colored illumination has beenemployed for many years. Presently, this is accomplished by rathercomplex lighting systems, as alluded to above, requiring the services ofa skilled operator to arrange the necessary combination of lightingcomponents to achieve a desired color or color pattern. Conventionallytheatrical lighting systems for this purpose include a light source witha plurality of solenoid-operated color filters for selective orientationin front of the light source for varying the color saturation with whichthe stage is illuminated. Such equipment may require several hundredcolor panels,and numerous light sources, all of which must be operatedby skilled personnel.

Certain of these problems have been alleviated to some extent by theprojection and display devices disclosed in the US. Pats. to Clark, 111No. 3,431,044; Lane et al. No. 3,315,391; and Billings No. 2,600,962.The Clark device inherently involves a number of moving parts butlimited color variation. The potential color variations achieved by theClark device are limited by employment of a solid double refractivemember. The polarizing panels of the Clark arrangement, when crossed,would considerably reduce light transmittance.

A similar arrangement is shown in the Lane et al. reference in which theintermediate solid member is additionally deformed to simulate motion.The Billings device is analogous, except that a stress-responsivebirefringent crystal is employed. The Billings arrangement, moreover, isnot directed to the problem of aesthetic or decorative lighting, as itis arranged to pass very narrow optical bands.

In general, the variety of color patterns attainable with devices suchas disclosed by Lane et al and Clark is limited, owing to the employmentof birefringent solid members. In addition, the cited references requirethe use of various light polarizing structures, which are not essentialin certain forms of my invention.

1 overcome these disadvantages of the prior art by providing a uniqueoptical display device capable of producing an infinite variety of colorvariations and patterns. The solution to this perennial problem isrealized by introducing a liquid crystalline material into a displaydevice of novel construction. Desirably the liquid crystalline materialis selected which has a characteristic of variable light scattering andattendant transmittance at room temperatures or at least at thoseenvironmental temperatures under which the device is employed. Forexample, a liquid crystalline material can be selected, which is capableof such variable transmittance at operating temperatures in the regionof a projection bulb or other illuminating light source, for example oneutilized in an advertising sign or other display arrangement. Theselected liquid crystalline material preferably exhibits a variablescattering or transmitive characteristic when subjected to mechanicaldeformation, such as occasioned by shear or flow stresses.

Accordingly, my novel display device or liquid crystal cell is providedfirstly with a light transmitting wall to permit viewing of thecontained liquid crystalline material. Secondly, the liquid crystallinecell is associated with means for inducing mechanical stresses withinthe contained liquid crystalline material. This can be accomplished in avariety of ways: For examples, the liquid crystalline cell can beconstructed with means permitting the displacement of one wall structurethereof relative to another. Circulating means can be associated withthe cell or display device for inducing flow and attendant shearstresses within the liquid crystalline material.

My display device as thus far described is capable of a large number ofapplications, for example as an aesthetic novelty, decorative wall andtable top panels, back drops for stages and other illuminated areas, andnumerous analogous applications. For this purpose, background orenvironmental illumination is sufficient for viewing the infinitevariety of color patterns resulting from a stress-manipulation of mydisplay device.

1 also contemplate the use of polarizing means to enhance or modify thecolor patterns. One or two polarizing panels can be employed for thispurpose and at least one of the panels can optionally be secured to orprovided as a support for a film of the liquid crystal. Where the liquidcrystal is preferably enclosed in a display container, the polarizingpanel can be mounted on a light-transmitting wall structure of thecontainer or the panel can form the wall structure. Where a pair ofpolarizing panels are used, the liquid crystalline material can bemounted therebetween, with one or both panels forming at least part ofthe support or container for the liquid crystal. The two polarizingpanels can be crossed without impairing visibility of the color patternsexhibited by the liquid crystal, as a liquid crystal is selected in suchcase for the characteristic of circular dichroism. In one arrangement ofthe invention, the display device and the polarizing means or at leastone of the polarizing panels are arranged for relative rotation so thatthe observed color patterns can be varied both by applied deformationalstresses as well as by modification of the incident illumination.

In another arrangement of my invention, a synchronous motor can beprovided for operating the aforementioned color varying means (forexample the rotatable polarizing means or the mechanical stress varyingmeans, or both) in accordance with a timed or rhythmic sequence forsynchronizing my color display device with music or other rhythmicoperation. I also desirably provide means for cooling the liquid crystalcell when employed in conjunction with my novel projection arrangement.

My invention also contemplates means especially arranged for projectingor otherwise enhancing the aesthetic effects produced by my noveldisplay device. Such means includes a projecting and polarizingarrangement suitable for projecting the color patterns of my displaydevice upon a wall ofa room, a stage and/or its occupants, cinema-typescreen, or other surface on which an infinitely variable color patternsis desired for aesthetic, decorative or entertainment purposes. A largenumber of applications of my inventions in the advertising field forvarious types of eye-catching signs and displays will become readilyapparent.

My display device is capable of producing nonrepetitive color patternswhich are a mixture of natural hues and intensities. The effectsachieved are warm, relaxed, and psychologically subdued and aretherefore particularly desirable for decorative and other aestheticpurposes. 7

Besides its aesthetic values, my display device is useful in depicting,as a color display, relative motions between or among a number ofobjects. Such relative motions can be comparatively slight and even of avibratory nature. Of greater significance is the capability ofsimultaneous indication of a number of forces applied externally to mydisplay device at a given time.

I am aware, of course, of a number of United States patents relating tovarious applications of liquid crystalline materials. For example,Fergason et al., U.S. Pat. No. 3,] 14,836 depicts an imaging device,which exhibits a color pattern on a film of liquid crystal upon focusinga heat or thermal pattern thereon. Fergason U.S. Pat. No. 3,409,404discloses a liquid crystalline device in which variation in selectivescattering of liquid crystalline materials is employed for identifyingunknown materials. Williams U.S. Pat. No. 3,322,485 utilizes a thresholdcharacteristic of liquid crystalline material to scatter lightselectively in the presence of a given electric field. Freund et al.U.S. Pat. No. 3,364,433 employs a frequencyshifting characteristic ofliquid crystalline materials in the presence of an electric and/ormagnetic field. None of these references, however, discloses a colordisplay device utilizing liquid crystalline materials in which aninfinite or non-repetitive pattern is exhibited by a liquid crystallinematerial applied by attendant variation in applied mechanical stresses.

I accomplish these desirable results by providing a display device forpresenting a visual indication of pressure, said article comprising asupport capable of supporting a layer of liquid crystalline materialthereon, said material having a characteristic of selective lightscattering which is variable in accordance with applied deformationalstresses and means for applying deformational stresses to said material.

I also desirably provide a similar display device wherein said supportis a container having a lighttransmitting wall structure through whichsaid material can be observed.

I also desirably provide a similar display device wherein said stressapplying means include means for effecting a flow of said materialrelative to said container.

I also desirably provide a similar display device wherein said containeris fabricated entirely from a transparent material.

I also desirably provide a similar display device wherein said supportis a light-polarizing panel.

I also desirably provide a similar display device wherein additionallight-polarizing means are mounted adjacent said panel and means areprovided for relatively rotating said panel and said additionalpolarizing means.

I also desirably provide a similar display device wherein cooling meansare coupled to said circulating means for maintaining said materialwithin a temperature range at which said light scattering characteristicapproaches a maximum condition.

I also desirably provide a similar display device wherein said displaydevice is arranged for operation adjacent a source of infraredradiation, and a thermal shield is interposed between said support andsaid radiational source, said heat shield including a relatively flattransparent container substantially coextensive with said support topermit viewing of said material therethrough, and means for circulatinga coolant fluid through said shield container.

I also desirably provide a similar display device wherein projectingmeans are provided for said display device, said projecting meansincluding a light source and condenser and objective lens systems, meansfor supporting said display device between said lens systems, and alight polarizing filter is disposed between said display device and atleast one of said lens systems.

During the foregoing discussion, various objects, features andadvantages of the invention have been set forth, or alluded to. Theseand other objects, features and advantages of the invention togetherwith structural details thereof will be elaborated upon during theforthcoming description of certain presently preferred embodiments ofthe invention and presently preferred methods of practicing the same.

In the accompanying drawings I have shown certain presently preferredembodiments of the invention and have illustrated certain presentlypreferred methods of practicing the same, wherein:

FIG. 1 is an isometric view, partially broken away, of one form ofliquid crystal cell or display device arranged in accordance with myinvention;

FIG. 1A is a cross-sectional view of the device of FIG. 1 and takenalong reference line lA-lA thereof;

FIG. 2 is an isometric view of a similar display device provided inconjunction with rotatable polarizing means;

FIG. 3 is an isometric view of another form of display device of myinvention and incorporating modified means for inducing deformationalstresses within the liquid crystal;

FIG. 4 is a cross-sectional view of the device as shown in FIG. 3 andtaken along reference line IV-IV thereof;

FIG. 4A is a similar view of a modified form of the display device shownin FIGS. 3 and 4;

FIG. 5 is an isometric view of still another form of my display deviceand illustrating a further modification for inducing deformationalstresses, in this case in accordance with the timing sequence;

FIG. 5A is a cross-sectional view of the display apparatus shown in FIG.5 and taken along reference line VA-VA thereof; and

FIG. 6 is an isometric view of novel projection means incorporating adisplay device of my invention.

With reference now to FIG. I of the drawings, a display device 10 in theform of a liquid crystalline support 12 is illustrated therein. In thisarrangement, the support 12 in the form of a flat container havingapposed wall structures 14, 16 of any suitable size and shape. In thearrangement shown, the wall structures 14, I6 are substantiallycoextensive although this is not an essential requirement. In point offact, one of the wall structures l4, 16 can be significantly smallerthan the other wall structure, as long as one wall structure is joinedabout its periphery to the other wall structure, for example in themanner described below. Likewise, the wall structures 14, 16 need not beof square or rectangular configuration as illustrated but can be of someother configuration for example circular as illustrated in FIG. 3. It iscontemplated however, that any geometrical or non-geometrical,symmetrical or nonsymmetrical shape can be employed for either or bothof the wall structures l4, 16. As noted previously, the wall structures14, 16 need not be coterminous. Further, the wall structures 14, 16 neednot be planar as shown in FIG. 1A but instead one or both sides thereofcan be dished or otherwise configured as indicated in FIG. 4.

Depending on the manner in which the wall structures 14, 16 are joined,the resilience and hence the thickness of either or both of the wallstructures l4, 16 may or may not be critical. Such criticality, whetherencountered depends on the manner in which deformational stresses are tobe applied to a liquid crystalline material 18 confined between the wallstructures 14, 16. In the arrangement of my novel display device asillustrated in FIG. 1, at least one of the wall structures 14, 16 issufficiently thin or is made of a suitably plastic material as to lend aresilient character to the wall structure. Thus, the wall structure,such as the wall structure 16 can be bent or otherwise deformed towardthe wall structure 14 when a force is applied more or less transverselythereto as denoted by arrow 20. By thus bending one of the wallstructures l4, 16 relative to the other, the liquid crystalline material18, which is supported, in this example, between the wall structures 14,16 in film-like form, is caused to flow generally away from the regionof applied force (arrow 20) to other regions of the volume confinedwithin the liquid crystal support 12. The application of the force 20and the resultant flow of the liquid crystal l8 develops shear and otherdeformational stresses within the liquid crystal 18. Such stressesmodify the light scattering and attendant transmittance characteristicsof the liquid crystal material 18 and result in an endless variety ofcolor changes and patterns.

In order to observe these aesthetic color changes, at least one of thewall structures 14, 16 is light transmitting, and preferably both of thewall structures 14, 16 are light transmitting to permit the displaydevice 10 to be observed from either side thereof. Desirably, both ofthe wall structures l4, 16 are made transparent for optimum visualcharacteristics, as when the display device 10 is employed in theprojection arrangement of FIG. 6.

As noted previously, at least one of the wall structures 14, 16 isjoined about its periphery to a surface of the other wall structure. Inthe FIG. 1 arrangement such joining means are further arranged toperipherally seal one wall structure to a surface of the other. In thedisplay device 10, such joining and sealing means includes apressure-sensitive tape 22, which is compatible with the material of thewall structures 14, 16 and covers their coextensive peripheral edges.The liquid crystal 18 is thereby sealed in the context of filmthicknesses within the space defined by the slightly separated wallstructures 14, 16 and the peripheral tape 22. It will be understood, ofcourse, that the separation between the wall structures 14, 16 can bedifferent from that illustrated, depending upon the relative quantity ofliquid crystal 18 which is used. Generally, a relatively thin film ofliquid crystal 18 should be enclosed between the wall structures 14, 16to conserve the liquid crystalline material.

In those cases wherein the joining and sealing tape 22 is quite flexibleand more or less loosely applied at the wall edges or is at leastsomewhat elastic, one or both of the wall structures 14, 16 can be madethicker and hence less resilient. In such cases, an eccentricapplication of the deformational force 20 will cause one of the wallstructures to become slightly canted or angulated or otherwise displacedrelative to the other in order to induce deformational flows in theliquid crystalline material. Such deformational flows are, of course,aided by the elasticity and/or edge slackness of the joining and sealingtape.

The liquid crystalline material 18 is selected from one or more of thosematerials which exhibit variation in light scattering and attendanttransmittance characteristics under deformational stresses. Desirably,such variations are within the visible range at room temperatures or atwhatever ambient temperature conditions prevailing in the area ofutilization of the display device 10. As an example of the lattersituation, the liquid crystalline material 18 can be one of those whichexhibit visual stress variation in the aforementioned characteristics ator near body temperature, and is therefore useful when the displaydevice is held in the observers hand. Larger display devices 10 can ofcourse be bathed with infrared radiation, if their liquid crystals arenot of the room temperature visual variety.

On the other hand, display devices for outdoor use, as for signs andother advertizing situations, require liquid crystalline materialsexhibiting stress indicia at correspondingly lower temperatures.

There are a considerable number of substances which exhibit thecharacteristics required of the liquid crystalline material 18. Ingeneral the category of materials known as cholesteric liquid crystalsare suitable for use with my invention and exhibit an optical phenomenonknown as selective scattering of white light. The appellation of thiscategorization of liquid crystals originates in the frequent use ofcholesterol as the starting material in synthesizing these organicsubstances. The derivatives of cholesterol usually are liquidcrystalline in character and demonstrate the characteristic of selectivelight scattering. Liquid crystalline substances fall additionally intothe general chemical classifications of esters, carbonic esters,eithers, schiff bases, and related classes. Nominally, the cholestericliquid crystals are not limited to the use of cholesterol as a basematerial. Many steroids exhibit similar optical characteristics whensynthesized into the general classifications of organic compounds, asmentioned above. These and other cholesteric" liquid crystals are usefulfor the purposes of my invention as long as their molecular conformationexhibits the necessary anisotropic and optical characteristics.

For the purposes of my invention, I employ a cholesteric liquidcrystalline material which exhibits a relative optical phenomenonattendant to the selective scattering characteristic of this category ofliquid crystal. The latter characteristic is the stress or shearsensitivity of certain cholesteric materials whereby the selectivescattering characteristic is varied upon the application ofdeformational stresses.

Cholesteric materials will selectively and visibly scatter white light,at or near room temperature conditions, when two or more of thesesubstances are admixed in proper proportions. Mixtures of liquidcrystals can be selected or varied to obtain visual responses at othertemperatures for the purposes mentioned previously. It is observed thata physical deformation of the liquid crystal will shift the frequency ofthe observed cholesteric color display or pattern,.when viewed at agiven angle, toward the blue or shorter wave length end of the visiblespectrum. The amount of color shift, measured in wave length units, canbe employed to indicate quantitatively the physical stress applied tothe cholesteric material, when a given liquid crystalline material hasbeen properly calibrated.

A constant pressure applied to the liquid crystalline material will not,after its initial application, thereafter appreciably effect the thenobserved color patterns. instead, the great variety of color changes orpatterns exhibited by my display device are produced by changes inapplied forces and attendant deformational stresses. With accelerationof changing deformational stresses, in either direction, changes in theobserved color patterns become more pronounced.

it has also been observed that the application of a constantdeformational stress over a significant period of time will initiallyinduce an observable change in the cholesteric color pattern, whichdespite continued stress, will revert to the unstressed or originalcholesteric color in time. That is to say, there is a relaxationaleffect in the liquid crystalline structure, owing to its nature.

It will be understood herein that a cholesteric substance is one whichamylcyanobenzylidineaminocinnamate in the cholesteric state at a certaintemperature. The cholesteric state of such substance exists in theregion between the temperature at which the substance behaves as a trueliquid and the temperature at which the substance is a solid. In thecholesteric state the substance is optically negative, has a strongrotatory power, selectively scatters light to give vivid colors (ormonochromatic light to give areas of darkness and brightness), andexhibits circular dichroism. Such a physical state is especially notablein derivatives of cholesterol andlike materials, although a relativelyfew other substances such as optically activeamylcyanobenzylidineaminochinnamate and the aforementioned steroidsexhibit the cholesteric state.

The liquid crystalline substances herein contemplated will be in thecholesteric state within at least a certain temperature range, but asthe temperature is raised above, or depressed below, this range thesubstances will pass into another mesomorphic state or into a normalliquid or solid state. Thus, the cholesteric substance will be in thecholesteric state at a first temperature and will change its phase intosome other state at a second temperature. Generally, it is preferred inthe practice of this invention that the second temperature be higherthan the first temperature. The range of temperatures within which avisible color display is exhibited as a result of scattering of whitelight can be determined by a proper selection of cholesteric substancesand will be referred to as the color play range.

Cholesteric substances used according to the present invention can bechosen from a wide range of compounds exhibiting the cholesteric phase.Derivatives of cyclopentanophenanthrene are desirably used. There are anumber of factors to be considered in selecting such derivatives: All ofthe ring systems should be in the trans configuration, the 3-substituent(on the A ring) should be in the B-configuration, and there should be nomore than two axial methyl groups. Unsaturation at the five, six carbonatom bond can have an effect on the melting point, but otherwise haslittle effect on the formation of the cholesteric phase. Thus,derivatives of such cyclopentanophenanthrenes as cholesterol,campesterol, ergosterol, B-sitosterol, stigmasterol, and like materialscan be used.

It is preferred in the present invention to utilize alkyl and arylderivatives of the cyclopentanophenanthrene materials, particularlythose derivatives which are esters of alkanoic or aralkanoic acids, ormixed alkyl esters of the cyclopentanophenanthrene material and carbonicacid. The alkanoic acids used can contain from one to 24 or more carbonatoms in the molecule, and can be saturated or unsaturated and straightor branched chain. It is preferred to utilize esters comprising higherfatty acids containing from 9 to 22 carbon atoms or lower saturated orunsaturated phenalkanoic acids having 1 to 3 carbon atoms. Mixedcarbonate esters comprising alkanols having from 1 to 22 carbon atomsand cholesterol are also among the preferred cholesteric substances.

Such derivatives of cholesterol are presently preferred in certainaspects of the invention. Thus, useful cholesteric substances includecholesteryl nonanoate, cholesteryl caprylate, cholesteryl laurate,cholesteryl palmitate, cholesteryl stearate, cholesteryl arachidate,cholesteryl behenate, cholesteryl oleate, cholesteryl linoleate, andcholesteryl linolenate, cholesteryl benzoate, cholesteryl cinnamate,cholesteryl dihydrocinnamate, and the like. Carbonate esters such asoleyl cholesteryl carbonate, stearyl cholesteryl carbonate, methylcholesteryl carbonate, ethyl cholesteryl carbonate, pentyl cholesterylcarbonate, and the like carbonates are very useful in the presentinvention.

It will be appreciated by those skilled in the art that a purecholesteric substance may have only a narrow color play range. However,where this color change does not occur at the temperature of interest,several stratagems permit coverage of a broad range of temperatures fromC, and even down to 40 C, up to and above 250C. One method of varyingthe color play temperature range is to prepare a substance at a desiredpurity level, as increased impurities usually lower the temperaturerange. One convenient method of carrying out this adjustment is to admixa plurality of chemically distinct cholesteric substances havingdifferent color play temperature ranges until the desired temperaturerange is obtained. Another method of adjusting the color play range isto prepare the substance in a highly purified form and to admix enoughof a less refined aliquot or aliquots of the substance with the purermaterial until the desired change of color play range is obtained. Forinstance, in this latter aspect, a 99.99 percent pure cholesteryl oleylcarbonate can be prepared and admixed with less refined material. Thoseskilled in the art will have no difficulty in providing a desiredtransition temperature for use in the compositions and articles of thepresent invention. All parts, proportions, percentages and ratios hereinare by weight unless otherwise stated.

The following tabulation will exemplify a few of the many color playregions obtained with the cholesteric substance or substances:

Substance(s) Color Play Region (C) 80% Cholesteryl oleyl carbonate 4 20%Chglesteryl acetate I 9592 cholesteryl oleyl carbonate 5'1 Chglesterylac etat e 1648 65% cholesteryl oleyl carbonate 259i Cholesterylnonanoate 7 l0; (fl elesteryl benzoate I 45% Cholesteryl oleyl carbonate45% Cholesteryl nonanoate 265-305 10% cholesteryl benzoate Cholesterylcinnamate 180-260 80% Cholesteryl nonanoate Z9% le 3L J P e" F5 1 45-6520' Cholesteryl butyrate 55 75 80% Cholesteryl nonanoat e 20%cholesteryl methyl carbonate 2247 09! Cholestery l n o&noate 90%cholesteryl cinnamate lO'i Cholesteryl nonanoate 40-250 cholesterylbenzoate 146-178 Choleateryl butyl carbonate 45-below 0 20! cholesteryldihydrocinnamate P05 Cholesteryl nonanoate It will accordingly beappreciated that one, two or more cholesteric substances can be mixed toobtain the requisite color play temperature range, and that both thetemperature and the range of temperatures can be widely varied. It isdesirable that the cholesteric substance(s) not crystallize at thelowest temperature at which they are held before use.

As disclosed above, a desired melting range can also be obtained byvarying the purity of cholesteric substances. It is usually found thatincreasing the purity raises the temperature of the color play regionand a narrowing of the range is also frequently obtained. It will, ofcourse be appreciated that the presence of excessive quantities ofimpurities will ultimately entirely prevent obtaining of the cholestericphase, especially if the impurities themselves are not cholestericsubstances. The cholesteric substance(s) can also comprise up to 5percent or so of miscible materials such as fatty acid triglycerides tolower the range. As disclosed hereinafter, it is most desirable toprotect the cholesteric substance from the milieu to obviate theimbibition of impurities by the cholesteric substances and thereby tomaintain the desired color play temperature.

As an illustration, cholesteryl oleyl carbonate is prepared as describedin Detection of Liquid Crystals," AD U.S. Pat. No. 620 940, US.Department of Commerce (August 1965). A portion of the cholesterylderivative is purified by solvent extraction and washed with methanol.The purified cholesteryl material is found to have a color playtemperature of 2l-22 C. Admixing parts of this material with 20 parts ofan unpurified material provides a color play temperature of 15 -16 C.

The cholesteric materials for use with this invention can also include acholesteryl halide. Although cholesteryl fluoride can be prepared, thedesired halides for use herein are cholesteryl chloride, cholesterylbromide, cholesteryl iodide, and mixtures of these halides. Thepreferred halide for use herein is cholesteryl chloride.

The cholesteryl halide serves to provide a uniform color over a broadrange of temperatures in which the cholesteric substance or substancesare in the cholesteric phase. Thus, in such case, my novel displaydevice shows a single color below transition to the condition whereinthe liquid crystal does not scatter visible light, i.e., the conditionin which it becomes colorless. The color below the transition point canbe selected according to the amount of cholesteryl halide used. As thequantity of halide is increased from about 15 percent of the compositionup to above 40 percent, the color usually varies from deep violet todeep red. The quantity of halide used will also vary according to theparticular cholesteric substances utilized. It has been found, however,that this color also varies according to viewing angle, depth of theliquid crystal layer, and the aforementioned deformation stresses, allof which, when combined with my display device, produced an interestingand unexpected variety of color patterns.

These halides are conveniently prepared by refluxing the cholesterolwith an excess (twice or more, stoichiometrically) of a thionyl halidefor 48-72 hours and distilling the mixture thereafter to removeunreacted material. Generally, the purity of the halides is sufficientto permit the desired change of phase from the cholesteric. It ispreferred that the halides be at least percent pure. Such halidesusually have a tendency to raise the color play temperature range of thecholesteric substance(s).

Specific examples of liquid crystalline compositions useful for mypresent invention appear below, wherein all amounts are in parts, ChClis cholesteryl chloride melting at 94-95 C; High ChOlC" is cholesteryloleyl carbonate showing a color play at 20-22 C; Low ChOlC ischolesteryl oleyl carbonate showing a color play at -6 C; ChNo ischolesteryl nonanoate; and the temperature is that at which thecompositions become colorless.

High Low Example ChCl ChOlC ChOlO ChNo Temp. l 27 73 42C. ll 27 58 I5455C. Ill 27 50 23 38C. IV 27 59 I4 35C. V 25 75 48C.

or the like, at least one of which is rotatable relative to the displaydevice One form of such polarizing means includes rotatably mounted disc24 supported on shaft 26 which is rotated in this example by a handcrank 28 through a suitable transmission denoted generally at 30.Obviously, the shaft 26 can be motordriven instead. In this arrangement,the polarizing disc or panel 24 is of polaroid material as noted above.

Instead of rotating the disc 24, the liquid crystal container 12'obviously can be rotated instead. In any event, such relative rotationof the display device 10' relative to the polarizing means 24effectively varies the angle of impinging illumination and therebyeffects a gross color change in the variable color patterns produced bythe display device 10 when subjected to the more or less transversedeformation forces as denoted by arrow In the arrangement of myinvention as disclosed in FIG. 2, then, a great variety of colorpatterns can be produced in the display device 10' through theapplication of transverse forces 20'. At the same time or sequentially,gross color changes in the produced color patterns can be effected byrelative rotation between the polarizing disc 24 and the liquid crystalcell 12'. The unusual and unexpected results thus produced areengendered by the unexpected cooperation between the polarizing disc 24and the inherent circularly polarizing characteristic of the liquidcrystalline material 18'. This characteristic, or dichroism, is presentin varying degrees in the aforementioned liquid crystalline materials.

A second polaroid panel or disc (or equivalent polarizing means)desirably is disposed on the other side of the container 12'. Thecooperative effect of the polarizing panels and the dichroic characterof the liquid crystal greatly and surprisingly enhances the vividness ofthe visual liquid crystalline color patterns and the changes wroughttherein by stress variations. Ancillary to such cooperation is thesignificant fact that the intensity of the visual color display is notdiminished, when the polarizing panels (at least one of which isdesirably rotatable, when two are used) are crossed, owing to thedichroic characteristic.

With two polarizing media, one medium desirably is incorporated withinthe structure of the liquid crystal container 12', as by forming one ofthe wall structures 14 or 16' of polaroid or other polarizing material.Desirably that wall structure (e.g. the wall 16' in FIG. 2) removed fromthe external polarizing filter 24 (if used) is so constructed so thatthe liquid crystal 18' is advantageously disposed between the polarizingmeans. If rotation of the polarizing is not desired, the externalpolarizing filter 24 can be omitted and both wall structures can befabricated from light polarizing material with a constant butadvantageous enhancement of color patterns. 1

Another form of my color display apparatus 32 is illustrated in FIGS. 3and 4. The liquid crystal container 34 forming part of display apparatus32 is of modified construction in that it does not depend on thefunctional displacement of one wall structure relative to another.Instead, the liquid crystal container 34 can be formed from a relativelyrigid housing, including in this case bipartite components 36, 38provided with inwardly dished surfaces 40 as better shown in FIG. 4. Anysuitable structural material can be employed for fabricating the housingcomponents 36, 38 although at least one of the components is fabricatedfrom a light transmitting material. Accordingly the housing components36, 38 can be fabricated from glass, plexiglass, or other material oftransparent or translucent character.

A quantity of liquid crystalline material 18" is sealed between thehousing components 36, 38 as evident from FIG. 4. This is accomplishedby peripherally joining the thickened edge portions 42 of the housingcomponents 36, 38 by means of a suitable cement. In the event that thehousing components 36, 38 are fabricated from certain plastic materialssuch as poly methacrylic resin, the thickened portions 42 of the housingcomponents can be joined by heat-sealing or solvent welding.

In order to create a variety of varying color patterns within the liquidcrystalline material 18" thus enclosed within the cell 34, means areprovided for inducing fluid flows and attendant deformational stresseswithin the body of the liquid crystalline material 18". As mentionedabove with reference to FIG. 1, the resultant shear and otherdeformational stresses lead to the changing color patterns of the liquidcrystal. One arrangement for so inducing flow of the liquid crystal 18"includes means for circulating a quantity of liquid crystalline materialthroughout the volume enclosed by the housing components 36, 38. Infurtherance of this purpose, the housing components 36, 38 define a pairof opposed flow apertures 44, 46 when assembled as aforesaid.Alternatively, the flow apertures 44, 46 can be bored in the liquidcrystalline container 34 after assembly thereof. The apertures 44, 46provide in this example egress and ingress of liquid crystal relative tothe container 34.

To circulate liquid crystalline material 18" throughout the container34, a pair of conduit sections 48, 50 are joined to the container 34 asshown. Such joining can be effected by threading the ends of the conduitsections 48, 50 and tapping the apertures 44, 46 or by cementing closelyfitting ends of the conduit sections 48, 50 into the apertures 44, 46 orby other suitable securance means.

The conduit sections 48, 50 are joined to the inlet 52 and outlet 54respectively of a circulating pump 56,

which is rotated in this example by a suitable prime mover such aselectric motor 58. For smaller sizes of display apparatus 32 and theircorrespondingly smaller pumps, a manually operated crank (not shown) canbe provided. Operation of the pump 56 circulates the liquid crystalmaterial 18" through the conduit sections 48, 50 and of course at acorrespondingly slower rate through the liquid crystal container 34. Thecirculation thus afforded by the pump 56 can be faster or slowerdepending upon the particular sequence of changing color patterns whichis desired.

The flow patterns desirably are spread out across the face 60 of theliquid crystal container 34 by suitable flow baffle means. One form ofsuch flow baffle means includes a pair of V-shaped baffle members 64, 62mounted as shown near the outlet and inlet apertures 44, 46 of the cell34. Other shapes of baffle members can be substituted for the particularbaffle members 62, 64 depending upon the flow characteristics desiredwithin the container 34.

For enhancement of the changing color patterns of the liquid crystal18'', the container 34' can be associ ated with suitable polarizingmeans arranged in accord with the exposition of FIG. 2. As shown in FIG.4A a polarizing disc 66 or 68 can be supported at either side of thecell 34. One or both of the polarizing discs 66, 68 can be utilized. Ina particular arrangement of the invention, wherein both housingcomponents 36', 38' are made transparent, the use of both polarizingdiscs 66, 68 is preferred. The discs 66, 68 desirably are mounted on theouter surfaces of the container 34, i.e., housing components 36', 38respectively. In furtherance of this purpose each of the discs can beprovided with a pressure-sensitive light-transmitting adhesive on oneside thereof so that the disc 66 or 68 can be adhered directly to thejuxtaposed face of the liquid crystal container 34'. Desirably, theadhesive characteristic of at least one of the polarizing discs 66, 68is ofa lesser order so that the polarizing discs can be readily peeledoff and reoriented upon the liquid crystal container 34' to effect agross change in its color patterns, the variable nature of which isdependent primarily upon the flow of liquid crystal through the conduitsections 48', 50'.

In the event that the liquid crystal container 34 or 34' will be used inmy projection arrangement of FIG. 6 as described below, or in otherareas of high ambient temperature, means can be conveniently associatedwith the circulating system of the display device 32 for cooling theliquid crystalline material. Cooling becomes necessary when the liquidcrystalline material 18 is exposed to an ambient temperature sufficientto cause the liquid crystalline material 18" to assume an isotropicstate resulting in loss of its selective light scatteringcharacteristic. One form of such cooling means includes a cooling jacket70 or other suitable heat exchanging means associated withat least oneof the conduit sections, for example the conduit section 50, as shown inFIG. 3. Cooling water from a suitable source (not shown) can becirculated through the cooling jacket 70 by means of inlet and outletconduit sections 72, 74. A requisite quantity of heat transmitted to theliquid crystal 18" through either face of the liquid crystal cell 34,and also any pump-work heat added to the liquid crystal circulatingsystem by the pump 56, can be removed by the heat exchanger 70. The heatexchanger 70 can, of course, be omitted from the display device 32 inthose applications not subjected to significant inputs of heat.

It falls within the contemplation of my invention that the deformationalstresses applied to the liquid crystal can be modified in accordancewith a predetermined sequence to provide a sequenced series of colorpattern changes. Thus, the transverse force 20 or 20' (FIGS. 1 and 2)can be so varied or modulated, and likewise the flow patterns throughthe container 34 or 34' (FIGS. 3 and 4A) can be similarly modified by asequential speed variation of the pump 56. It is contemplated furtherthat the aforementioned sequential variation of deformational stressescan be given a rythmic response so that the changing color patterns ofmy display device can be set to a suitable background music, balletperformance or other choreography, marching procession, or otherrhythmic activity.

One arrangement for thus effecting a rhythmic or other sequentialapplication of deformational forces is illustrated in FIG. 5. In thisarrangement, a liquid crystalline container 76 of the display device 78is constructed generally similar to the cell 34 of FIGS. 3 and 4. In thecontainer 76, however, its components 80, 82 are continuously sealed andjoined above their peripheries save for a single plunger opening 84, asbetter shown in FIG. 5A.

A plunger 86 is protruded through the plunger opening 84 for the purposeof inducing deformational stresses within the liquid crystal 88 in themanner described more fully below. Desirably the plunger 86 isfabricated from a transparent or light transmitting material to offer aminimal interference to the changing color patterns induced in theliquid crystal 88. Means desirably are provided for sealing the plunger86 to the container 76 to prevent loss of liquid crystalline materialand the entrance of foreign matter. A suitable sealing arrangementincludes a bellows 90 which is peripherally joined and sealed at one ofits ends to the adjacent portion of the plunger 86 and at its other endto the container 76. Use of the bellows 90 permits reciprocation of theplunger 86 while effectively maintaining a sealed environment for theliquid crystal 88. The flow induced within the liquid crystal 88 by theplunger 86 can be enhanced by means of one or more cross arms 98 securedto the plunger 86 (FIG. 5). Means are provided by my invention forreciprocating the plunger 86 in order to induce a flow characteristicwithin the liquid crystal 88. Where the displacement of the plunger 86,by its reciprocation, is relatively larger with respect to the volume ofliquid crystal 88, one of both of the cell housing components 80, 82 canbe made resilient to accommodate the corresponding volumetric changes.The aforementioned plunger reciprocation can be synchronized inaccordance with a predetermined timed or timing sequence in furtheraccord with my invention. This permits the varying color patterns of thedisplay device 78 to exhibit a sequentially timed or rythmiccharacteristic. Such characteristic in certain applications amy ofitself be a desirable feature of the aesthetic display or decorativeeffect produced by the display device 78. In other applications, asaforesaid, the rythmic characteristic permits the varying color displayto be set to music or other rythmic activity.

One arrangement for thus reciprocating the plunger 86 includes a wheel92 having a sinusoidal edge contour 94 or the like and rotatablysupported adjacent the outward end of the plunger 86 for successiveengagement between the plunger 86 and contoured edge of the wheel 92.The contour rises' 94, depending upon the particular application of thedisplay device 78, can be uniformly spaced (as shown) about theperiphery of the wheel 92 or they can be both of non-uniform spacing andof non-uniform heights (not shown) to afford a maximum variety andchange in the color patterns of the display device. However, if thecolor display is to be set to music or other rythmic activity, the wheel92 desirably is rotated at a uniform angular velocity, as dictated bythe measured beat of such activity, by suitable motive means such aselectric motor 96. It is contemplated, of course that a non-uniform,fast or slow rotation of the wheel 92 can be effected, depending uponthe particular sequence pattern change which is desired.

With the display devices described thus far, it is contemplated thattheir sizes can be made small enough to fit in a persons hand, oralternatively, the display arrangement can be made sufficiently large asto cover entire wall surfaces or door or window areas. That is to say, aliquid crystal "cell" can be made of sufficient length and width tocover part or all of a wall surface, ceiling, table top or otherfurniture surface, stage backdrops, or the like.

Alternatively, again, any of the liquid crystal devices described abovecan be provided with dimensions similar to that of a conventionalphotographic slide for projection on a screen or wall surface. Onearrangement of a suitable projection means 100 for accomplishing this isillustrated in FIG. 6 and utilizes a liquid crystal container or cell76' similar to that shown in FIGS. 5 and 5A. The plunger 86 can beoperated after the manner of FIG. 5 by the cog-wheel and motorarrangement 92-96 (not shown in FIG. 6) or alternatively the plunger 86'can be manipulated manually. The container components 80, 82' are bothlight-transmitting and desirably are transparent.

The liquid crystal cell 76' in the illustrated projection arrangement issupported by a suitable bracket 101 between a pair of polarizing filters102, 104. At least one of the filters, for example the filter 102, canbe rotated relative to the liquid crystal cell 76' and remaining filter.The assembly as described thus far in turn is supported between acondensor lens system denoted generally by lens 106 and an objectivelens system denoted similarly by lens 108.

In operation, light from a suitable source such as projector lamp 110 isfocused onto the liquid crystal cell 76 after passing through theinitial polarizing filter 102. The focused light falling upon the liquidcrystal cell. 76' is selectively transmitted therethrough and throughthe remaining polarizing filter 104 and is then projected upon asuitable wall surface or screen to reveal, in greatly enlarged form, thevarying color pattern of the liquid crystal cell 76. Means (not shown)desirably are provided for relatively moving the liquid crystal cell 76'and the objective lens 108 for focusing purposes.

The polarizing filters 102, 104 while not essential, are desirable forthe enhancement of the color hues and intensities evidenced by theliquid crystal cells 76, as noted previously. Variation in the projectedcolor pattern is effected by manipulating the plunger 86' to induce flowand deformational forces within the liquid crystalline materialcontained within the cell 76'. A gross color change can be superimposedupon the varying color patterns within the cell 76' by circularlydisplacing one of the polarized filters for example the filter 102.Manipulation of the filter 102 and the plunger 86 can be performedeither simultaneously or sequentially by the operator of the projectionarrangement 100.

To prevent loss of the variable light scattering characteristic of theliquid crystalline material, provision of suitable means for cooling theliquid crystalline material is desirable. Such means may take the formof this illustrated in FIG. 3, for example, where the plunger 86 isreplaced by a liquid crystal circulatory system.

On the other hand, a suitable and desirably transparent thermal shieldor screen 112 can be interposed between the liquid crystal cell 76' andthe light source to prevent the heat of the projector lamp from reachingthe liquid-crystal cell 76'. The heat screen 112 in this example can befabricated from a pair of transparent housing components, which can beconfigured similar to the housing component 36, 38 of the liquid crystalcell 34 shown in FIGS. 3 and 4 and preferably fabricated from a knownheat absorbing transparent material such as heat-absorbing glass.Desirably the heat screen 12 is no smaller in size and contour than thatof the liquid crystal cell 76. The housing components 114, 1 16 of theheat screen 112 can be fabricated from glass or plexiglass and joined inthe manner described above in connection with the components of any ofthe aforementioned liquid crystal containers. In this arrangement flowapertures are provided respectively at a pair of diametrically opposedcorners of the thermal shield 112, to which inlet and outlet conduitsI18, respectively are joined. The conduits 118, 120 are connected to asource (not shown) of water or other suitable coolant to effect a flowthrough the heat screen 112. A pair of baffle members 122 can beprovided adjacent the inlet and outlet openings of the thermal screen112 to spread the flow throughout the area enclosed by the housingcomponents 114, 116 thereof. Desirably, the flow baffles 122, arefabricated from a transparent material such as plexiglass.

From the foregoing, it will be apparent that novel and efficient formsof Variable Color Display Device and Projection Means Therefor have beendescribed herein. While I have shown and described certain presentlypreferred embodiments of the invention and have illustrated presentlypreferred methods of practicing the same it is to be distinctlyunderstood that the inven- .tion is not limited thereto but may beotherwise variously embodied and practiced within the spirit and scopeof the invention.

I claim:

1. An area color display device for presenting visual and variablycolored indications of variable pressure throughout said display area,said device comprising a container having a substantially rigid wallstructure and shaped to define and to enclose a thin layer of liquidcrystalline material when placed therein, said layer substantiallycoextending with said display area, said wall structure at leastcoextending with said liquid crystalline layer, said layer havingsufficient thickness that fluid flows can be induced in any givenportion or all of said layer, said container having a light-transmittingwall section through which said material can be observed, said wallsection being substantially coextensive with said layer, a quantity ofcholesteric liquid crystalline material contained within said containerand forming said layer, said cholesteric material having acharacteristic of selective light scattering which is variable inaccordance with applied deformational stress, means on said containeradjacent the periphery thereof for sealing said liquid crystallinematerial within said container, and means within said container forinducing volumetric flows in said material throughout said layer toapply said stress likewise throughout said layer.

2. The combination according to claim 1 wherein said liquid crystallinematerial includes at least one of the group consisting of alkylcarbonates and alkanoic esters of cholesterol, B-sitosterol,stigmasterol, and ergosterol.

3. The combination according to claim 1 wherein a quantity ofcholesteryl halide is admixed with said liquid crystalline material.

4. The combination according to claim 3 wherein said halide is presentin the amount of about percent to about 40 percent of the resultingcomposition.

5. The combination according to claim 1 wherein said container isfabricated entirely from transparent material.

6. The combination according to claim 1 wherein said container includesa second substantially rigid wall structure apposed to saidfirst-mentioned wall structure, and said stress applying means includeresilient joining and sealing means secured about the periphery of eachof said wall structures so that one of said structures can be displacedrelative to the other.

7. A display device for presenting visual indications of variablepressure, said device comprising a container having a substantiallyrigid wall structure and shaped to define and to enclose a thin layer ofliquid crystalline material when placed therein, said wall structure atleast coextending with said liquid crystalline layer, said layer havingsufficient thickness that uniform and nonuniform fluid flows can beinduced in substantially every part of said layer, said container havinga lighttransmitting wall section through which said material can beobserved, said wall section being substantially coextensive with saidlayer, a quantity of cholesteric liquid crystalline material containedwithin said container and forming said layer, said cholestric materialhaving a characteristic of selective light scattering which is variablein accordance with applied deformational stress, means on said containerfor sealing said liquid crystalline material within said container,means coupled to said container for inducing flow in said materialthroughout said layer to apply said stress likewise throughout saidlayer, said container including oppositely disposed inlet and outletapertures, and said stress applying means including circulating meanscommunicatively coupled to said container at said apertures foreffecting a flow of said material throughout said container.

8. The combination according to claim 7 wherein cooling means arecoupled to said circulating means for maintaining said material within atemperature range at which said pressure light scattering characteristicapproaches a maximum condition.

9. The combination according to claim 7 wherein flow baffle means areenclosed within said container and juxtaposed to said inlet and outletopenings, said baffle means being fabricated from a light-transmittingmaterial.

10. A display device for presenting visual indications of variablepressure, said device comprising a container having a substantiallyrigid wall structure and shaped to define and to enclose a thin layer ofliquid crystalline material when placed therein, said wall structure atleast coextending with said liquid crystalline layer, said layer havingsufficient thickness that uniform and nonuniform fluid flows can beinduced in substantially every part of said layer, said container havinga lighttransmitting wall section through which said material can beobserved, said wall section being substantially coextensive with saidlayer, a quantity of cholesteric liquid crystalline material containedwithin said container and forming said layer, said cholesteric materialhaving a characterestic .of selective light scattering which is variablein accordance with applied deformational stress, means on said containerfor sealing said liquid crystalline material within said container,means coupled to said container for inducing flow in said materialthroughout said layer to apply said stress likewise throughout saidlayer, said container including an opening, an agitator membersubstantially enclosed within said container and immersed within saidlayer, and said agitator member including a part protruding through saidopening for moving said agitator member relative to said material.

11. The combination according to claim 10 wherein said agitator memberis fabricated from a lighttransmitting material.

12. A display device for presenting visual indications of variablepressure, said device comprising a container having a substantiallyrigid wall structure and shaped to define and to enclose a thin layer ofliquid crystalline material when placed therein, said wall structure atleast coextending with said liquid crystalline layer, said layer havingsufficient thickness that uniform and nonuniform fluid flows can beinduced in substantially every part of said layer, said container havinga lighttransmitting wall section through which said material can beobserved, said wall section being substantailly coextensive with saidlayer, a quantity of cholesteric liquid crystalline material containedwithin said container and forming said layer, said cholesteric materialhaving a characteristic of selective light scattering which is variablein accordance with applied deformational stress, means on said containerfor sealing said liquid crystalline material within said container,means coupled to said container for inducing flow in said materialthroughout said layer to apply said stress likewise throughout saidlayer, said display device being arranged for operation adjacent asource of infrared radiation, a thermal shield interposed between saidcontainer and said radiational source, said thermal shield includingrelatively flat transparent containing means substantially coextensivewith said container to permit viewing of said container therethrough,and means for circulating a coolant fluid through said shield containingmeans.

1. An area color display device for presenting visual and variably colored indications of variable pressure throughout said display area, said device comprising a container having a substantially rigid wall structure and shaped to define and to enclose a thin layer of liquid crystalline material when placed therein, said layer substantially coextending with said display area, said wall structure at least coextending with said liquid crystalline layer, said layer having sufficient thickness that fluid flows can be induced in any given portion or all of said layer, said container having a light-transmitting wall section through which said material can be observed, said wall section being substantially coextensive with said layer, a quantity of cholesteric liquid crystalline material contained within said container and forming said layer, said cholesteric material having a characteristic of selective light scattering which is variable in accordance with applied deformational stress, means on said container adjacent the periphery thereof for sealing said liquid crystalline material within said container, and means within said container for inducing volumetric flows in said material throughout said layer to apply said stress likewise throughout said layer.
 2. The combination according to claim 1 wherein said liquid crystalline material includes at least one of the group consisting of alkyl carbonates and alkanoic esters of cholesterol, B-sitosterol, stigmasterol, and ergosterol.
 3. The combination according to claim 1 wherein a quantity of cholesteryl halide is admixed with said liquid crystalline material.
 4. The combination according to claim 3 wherein said halide is present in the amount of about 15 percent to about 40 percent of the resulting composition.
 5. The combination according to claim 1 wherein said container is fabricated entirely from transparent material.
 6. The combination according to claim 1 wherein said container includes a second substantially rigid wall structure apposed to said first-mentioned wall structure, and said stress applying means include resilient joining and sealing means secured about the periphery of each of said wall structures so that one of said structures can be displaced relative to the other.
 7. A display device for presenting visual indications oF variable pressure, said device comprising a container having a substantially rigid wall structure and shaped to define and to enclose a thin layer of liquid crystalline material when placed therein, said wall structure at least coextending with said liquid crystalline layer, said layer having sufficient thickness that uniform and non-uniform fluid flows can be induced in substantially every part of said layer, said container having a light-transmitting wall section through which said material can be observed, said wall section being substantially coextensive with said layer, a quantity of cholesteric liquid crystalline material contained within said container and forming said layer, said cholestric material having a characteristic of selective light scattering which is variable in accordance with applied deformational stress, means on said container for sealing said liquid crystalline material within said container, means coupled to said container for inducing flow in said material throughout said layer to apply said stress likewise throughout said layer, said container including oppositely disposed inlet and outlet apertures, and said stress applying means including circulating means communicateively coupled to said container at said apertures for effecting a flow of said material throughout said container.
 8. The combination according to claim 7 wherein cooling means are coupled to said circulating means for maintaining said material within a temperature range at which said pressure light scattering characteristic approaches a maximum condition.
 9. The combination according to claim 7 wherein flow baffle means are enclosed within said container and juxtaposed to said inlet and outlet openings, said baffle means being fabricated from a light-transmitting material.
 10. A display device for presenting visual indications of variable pressure, said device comprising a container having a substantially rigid wall structure and shaped to define and to enclose a thin layer of liquid crystalline material when placed therein, said wall structure at least coextending with said liquid crystalline layer, said layer having sufficient thickness that uniform and non-uniform fluid flows can be induced in substantially every part of said layer, said container having a light-transmitting wall section through which said material can be observed, said wall section being substantially coextensive with said layer, a quantity of cholesteric liquid crystalline material contained within said container and forming said layer, said cholesteric material having a characterestic of selective light scattering which is variable in accordance with applied deformational stress, means on said container for sealing said liquid crystalline material within said container, means coupled to said container for inducing flow in said material throughout said layer to apply said stress likewise throughout said layer, said container including an opening, an agitator member substantially enclosed within said container and immersed within said layer, and said agitator member including a part protruding through said opening for moving said agitator member relative to said material.
 11. The combination according to claim 10 wherein said agitator member is fabricated from a light-transmitting material.
 12. A display device for presenting visual indications of variable pressure, said device comprising a container having a substantially rigid wall structure and shaped to define and to enclose a thin layer of liquid crystalline material when placed therein, said wall structure at least coextending with said liquid crystalline layer, said layer having sufficient thickness that uniform and non-uniform fluid flows can be induced in substantially every part of said layer, said container having a light-transmitting wall section through which said material can be observed, said wall section being substantailly coextensive with said layer, a quantity of cholesteric liquid crystalline material contained within said container and forming said layer, said cholesteric material having a characteristic of selective light scattering which is variable in accordance with applied deformational stress, means on said container for sealing said liquid crystalline material within said container, means coupled to said container for inducing flow in said material throughout said layer to apply said stress likewise throughout said layer, said display device being arranged for operation adjacent a source of infrared radiation, a thermal shield interposed between said container and said radiational source, said thermal shield including relatively flat transparent containing means substantially coextensive with said container to permit viewing of said container therethrough, and means for circulating a coolant fluid through said shield containing means. 